Hybrid Routing and Forwarding Solution for a Wireless Sensor Network

ABSTRACT

A hybrid routing and forwarding solution for a mobile wireless sensor network is provided. This invention allows each node of the wireless sensor network to move in random directions in a three dimensional space. The invention seeks to minimize resource consumption while optimizing routing and forwarding in a wireless sensor network.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to routing and forwardingsolutions. More particularly, the present invention relates to a hybridrouting and forwarding solution for mobile or fixed wireless sensornetworks.

2. Description of Related Art

A wireless sensor network (WSN) is a self-organizing wireless networkthat consists of distributed devices with sensors commonly referred toas “nodes”. The sensors are application specific. They are used formonitoring environmental conditions, such as sound, temperature,vibration, pressure, motion or pollutants at different locations. Thewireless sensor network was originally motivated by militaryapplications. It is now widely used in many industrial, agricultural,medical and other civilian applications.

In addition to the sensors, each device in a WSN is equipped withelements such as a radio transceiver, microcontroller, flash memory,antenna, energy source and so on. A WSN device is typically low datarate, low cost and low power devices. The low cost of a WSN is aconstraint on system resources such as energy, memory, processor andbandwidth.

There are usually three types of WSN devices, i.e. the coordinator (orsink), router and end device. The first two devices have routingfunctionality. Both devices have ability to find proper routes toforward packets to desired destinations. An end device has no routingability, it only communicates with a specific router that is called theparent of the end device.

If the routing condition changes so that the original path becomesunavailable, the routers are able to find a new path to deliver thepackets to the destination. Currently, the WSN devices are usuallyinstalled in fixed locations. However, if the devices were installedinside a moving target, the routing among the wireless nodes becomes achallenge.

The routing protocols and forwarding processes are the major resourceconsumers of the software in a WSN. These modules require a good deal ofmemory, CPU time and a power resource. The wireless sensor nodes on theother hand, are typically low data rate, low cost and low power devices.Therefore, it is a challenge to provide routing and forwardingfunctionality in a WSN. Furthermore, it is an even bigger challenge in amobile WSN since the physical locations of the nodes are changeddynamically. The mobile WSN creates significant amount of variables andrequires extra resources and mechanisms.

Currently, there are many ways to implement routing and forwardingfunctionality in a mesh WSN. Most of them are data centric protocolsbecause an address centric (with unicast shortest path) approach iscommonly thought to take much more system resources and electric power.The data centric protocols usually are coordinator centric. They ignorethe roles of the individual nodes. Yet the forwarding path is lessdeterministic. Below are typical examples of existing approaches. Thefirst three are basically data centric, however the flooding mechanismworks in an address centric way as well:

1. Flooding the data over the WSN. This approach is simple but it cancreate implosion problems. The same copies are flooded over the areauntil they reach the destination.

2. Sensor Protocols for Information via Negotiation (SPIN). Thisprotocol forwards the data via negotiation that consumes less power thanflooding, but the SPIN is not reliable, it cannot guarantee the deliveryof the data.

3. Gossiping. At every step each node forwards data only to one neighborwhich is selected randomly. The neighbor must then forward the data backto the sender. The Gossiping avoids flooding but is inefficient.

4. AODV (Ad-hoc On-demand Distance Vector) based routing protocol. Thisprotocol uses route discovery and selection mechanisms. Its routerrequest and route reply process is effective, but not economical.

5. Conventional address centric shortest path routing. This approachfinds the shortest path and eliminates the flooding completely butrequires constant routing advertisement that is expensive and consumes agood deal of resources and electric power.

6. Typical solutions for mobile WSN: mobile base station basedsolutions, mobile data collector based solutions, and rendezvous basedsolutions. The restriction for these existing solutions is that all thenodes must be fixed except a coordinator node.

Therefore, what is needed is a method of routing and forwarding that mayefficiently allow intelligent and dynamic routing while eliminatingwaste. Moreover, the solution should allow for a mobile wireless sensornetwork.

SUMMARY OF THE INVENTION

The subject matter of this application may involve, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of a single system or article.

This invention seeks to meet the challenges described above by providingan innovative hybrid solution of routing and data forwarding in bothmobile and fixed mesh WSN.

The semantics of the hybrid property in this invention implies fouraspects. Firstly, it means a mix of broadcast and unicast forwardingthat work together to deliver the functionality; secondly, it allows thedata from the control plane and data plane to coexist in a single hybridpacket; thirdly, it provides both address centric and data centricprotocol features. Lastly, it supports both event driven and querydriven modes.

The event driven forwarding is usually triggered when the sensor nodesdetect something that must be reported. The data is sent unsolicited tothe coordinator or service center.

The query driven forwarding is triggered by a query from thecoordinator, service center, or any nodes within a WSN. The query issent periodically or randomly, it can be destined for a specific node, agroup of nodes or all the nodes over the area.

Note that there are specific limitations in a WSN due to hardware andsystem constrains. E.g. the distance between adjacent nodes andbandwidth of the nodes are restricted. For mobile WSN, the speed ofmobile nodes and the number of nodes moving simultaneously is limited.This is especially true when the traffic flows over a WSN frequently.

This solution is especially appropriate for a fixed or mobile WSN wherethe events or queries happen infrequently. However, it may work in anyWSN implementation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides an embodiment of a wireless sensor network.

FIG. 2 provides an embodiment of the formation of a unicast path basedon a broadcast from an initiator node.

FIG. 3 provides an embodiment of a multipoint to point unicast treebetween nodes rooted at the initiator node.

FIG. 4 provides an embodiment of node mobility and route adjustment.

FIG. 5 provides an embodiment of the processes that are taken when anode receives a query message from the coordinator.

FIG. 6 provides an embodiment of the processes that are taken when aquery data vehicle arrives on local node.

FIG. 7 provides an embodiment of the processes that are taken whenvehicle_q2's timer fires.

FIG. 8 provides an embodiment of the processes that are taken when amessage is ready to be sent out.

FIG. 9 provides an embodiment of the processes that are taken when awild card data vehicle arrives on current node.

FIG. 10 provides an embodiment of the processes that are taken whenvehicle_w2's timer fires.

FIG. 11 provides an embodiment of the procedures of the acceptance andloop check, and how an incoming broadcast packet is processed.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently preferred embodimentsof the invention and does not represent the only forms in which thepresent invention may be constructed and/or utilized. The descriptionsets forth the functions and the sequence of steps for constructing andoperating the invention in connection with the illustrated embodiments.

This invention provides a unique routing and forwarding solution for amesh WSN. It is powerful, efficient, flexible and reliable. Inparticular, it supports both fixed and mobile mesh WSN. The mechanismscreated in this invention are highly dynamic and time sensitive whichmakes it a good fit for mobile conditions and an appropriate solutionfor a mobile WSN. Existing WSN protocols limit the mobility of a WSN tothe coordinator only. In contrast, this solution extends the mobility toany Full Function Device (FFD) nodes in a WSN.

This invention uses a number of hybrid approaches to coordinatedifferent mechanisms intelligently so that the services are maximizedwhile the resource consumption is minimized.

This invention provides a unique hybrid approach with four flavors, i.e.a hybrid between broadcast and unicast forwarding; a hybrid betweenaddress centric and data centric features, a hybrid of control data anduser data in a single packet; and a hybrid of event driven and querydriven mode.

This invention utilizes a combination of broadcast and unicastforwarding. To generate a broadcast packet, one option is to encode userdata and routing advertisement in a single packet so that the unicastbest routes are created quietly while the broadcast packet reaches thedestinations. The unicast routes are destined for the initiator of thebroadcast. The initiator could be a coordinator or other node in thenetwork.

In a conventional network, the separation of the control packets anddata packets is essential, because the high speed forwarding becomesimpossible otherwise. Wireless Sensor Networks, however, are lowbandwidth, low speed networks. Data packets are extremely small,sometimes smaller than a control packet. Furthermore, the speed of thedata forwarding is not an issue. Therefore, the combination of a datapacket and control packet becomes feasible.

The routing advertisement usually consumes significant amounts of systemresource and electric energy. In general, it takes a full cycle of abroadcast to propagate a routing advertisement over an ad hoc network.This problem is compounded in that it happens periodically. The overheadis considerable.

FIG. 1 shows an embodiment of a WSN. The WSN consists of a plurality ofnetwork nodes including routers, shown as circles; end devices shown asstars; and a sink node shown as a triangle. These nodes are incommunication with each other. The sink node allows communicationdirectly to a central computer, or out to the internet. The networknodes are impacted by environment events which are sensed by the nodes.

This invention eliminates the regular routing advertisement. Thepropagation happens in a need base only and routing data is piggybackedby broadcast packets. In summary, this invention provides a way to enjoythe advantage of the unicast best routes without the huge overheads ittakes.

This solution further creates the concept of smart metrics that areencoded by conventional and real time information. The smart metric is aleverage that controls the forwarding process intelligently anddynamically. It can shape real time traffic and optimize the forwardingprocess. The unicast routes created during the broadcast represent thereal time best paths rather than the traditional shortest paths.

This invention uses unique, flexible smart metrics that control theforwarding process intelligently and dynamically. A number of flavorsmay be encoded into the smart metrics, for example: the number of hops,link quality and electric power reserved.

In one smart metric embodiment, to simplify the logics, the link qualitycan be measured with M levels. The M is the highest quality. Likewise,the reserved electric power is measured with N levels. N is the highestlevel. Both M and N values are configurable.

If an ordered set of nodes [N1, N2 . . . NL] defines path P, the numberof the nodes is L, the direct link [Ni, Ni+1] is a sub path of P, thenthe cost of path P is:

${C\left\{ P \right\}} = {{k\; 1\left( {L\text{-}1} \right)} + {k\; 2{\sum\limits_{i = 1}^{L - 1}\left( {{M\text{-}{LQL}\left\{ \left\lbrack {{Di},{{Di} + 1}} \right\rbrack \right\}} + {k\; 3{\sum\limits_{i = 1}^{L - 1}\left( {N\text{-}{PR}\left\{ {Di} \right\}} \right)}}} \right.}}}$

Where LQL{[Di, Di+1]} is the level of link quality between node Di andDi+1; PR{[Di, Di+1]} is the reserved power level of node Di; k1, k2 andk3 are the coefficients that are used to adjust the contributing levelof different flavors. The k1, k2 and k3 values are configurable, andmight be changed from application to application.

In this embodiment, the formula shows that the cost is lower if thenumber of hops is less, and if link quality and power reserving levelare higher. The link quality and power reserving level are changeddynamically, which in turn affects the smart metric dynamically.

This solution could be viewed as an address centric protocol to someextent. Indeed, this hybrid approach covers the features of addresscentric as well as data centric protocols. E.g. it allows a loose dataaggregation during the data forwarding. The data aggregation is afeature provided by data centric protocols. It reduces the number ofpackets traveling through a WSN. This solution allows the aggregation tobe in an arbitrary manner. Hence the forwarding processes becomeextremely flexible.

This invention supports a unicast best path in a unique way so that thelarge overhead of prior art route advertisement is avoided. In addition,the smart metric provides opportunities to optimize the routedynamically with real time information.

This invention supports mobile WSN that allows the coordinator and otherFFD nodes to move in any direction. Note that the mobility is usuallylimited to the coordinator only in the WSN routing protocols of theprior art.

The broadcast mechanisms in this invention are distinct from existingapproaches. Examples of the differences may include:

A loose aggregation of the user data reduces the number of packetsflowing over the WSN without sacrificing any functionality. Thisaggregation is arbitrary so the flexibility of the process is maximized.

A broadcast flooding is considerably expensive. In this invention, thebroadcast is triggered by an event or query only. Furthermore, abroadcast packet can piggyback routing advertisements.

This invention excludes the constant route advertisements and routediscovery processes.

A regular routing advertisement takes a full cycle of a broadcast in anad hoc network and it happens constantly. A route discovery mechanismtakes two way processes, i.e. a broadcast forwarding in one directionand a unicast forwarding in reverse direction.

In the present invention, the broadcasting is optimized. The forwardingloops are completely eliminated and the same packet will not berepeatedly broadcasted by each node.

During the broadcasting, multiple copies can be forwarded over a WSN.This is an overhead. In this invention, some overhead is unavoidable.However, broadcast overhead is used to increase the reliability of thetransportation.

Unlike most of the routing protocols, this invention excludes theconstant route advertisements and route discovery processes. Thisapproach dramatically reduces the consumption of electric power and CPUresources. In a typical Wireless Sensor Network, the transmission of apacket consumes several times of electric power that a CPU consumes atsame time. The constant route advertisements and maintenances are themost expensive software processes within a WSN device. The routediscovery is a considerable overhead as well.

This invention uses a hybrid approach of broadcast and unicastforwarding and a hybrid approach of routing advertisement and dataforwarding in one packet. The broadcast packet plays two roles: the datadelivery and routing advertisement. In particular, the broadcast sessionis driven by the events and queries. The unicast session is usually forthe sensor nodes to forward their responses to the querist.

In this invention, the unicast routes are usually not maintained beforesending a query message or an unsolicited event since conventionalrouter advertisements and discovery mechanisms are excluded. Instead,this invention broadcasts query messages or unsolicited events over theWireless Sensor Network until the messages reach the desireddestinations.

It is uncommon to broadcast the user data in conventional network,nevertheless a query or event message is as small as a typical controlpacket in a Wireless Sensor Network. The total cost to broadcast a queryor event message is similar to a single run of route advertisement. Thecost is less than a router discovery process considering the discoveryprocess is a two way process with the broadcast in one direction andunicast in reverse direction.

It should be noted that the broadcast for conventional distance vectorroute advertisement is processed at a regular basis. Alternatively, thebroadcast performed with this invention is at a need basis. The routediscovery process is also at a need basis, but it does not contribute todata transmission. It is an overhead when the process could be excluded.In general, applications that conduct infrequent queries and unsolicitedevent messages take the most of the advantages of this invention interms of power and resource saving.

In this invention, a broadcast packet includes routing section and anapplication section. The routing section has all the flavors of routingadvertisement in a typical distance vector routing protocol. Theapplication section accommodates various user data, such as a querymessage or an event report message. While receiving a broadcast packet,the routing module of a node processes the routing section, this issimilar to a distance vector routing protocol. The application layerprocesses the application section based on application details.

The broadcast packet is transferred from a node to its neighbor justlike a conventional broadcasting. A unicast route toward the initiatorof the broadcast is created during the broadcasting. The route isrefined during propagation. The best next hop is selected and installedin the forwarding table. The selection of the path is determined by asmart metric that is decided by, for example, number of hops, the linkquality, and power level etc. A timer or a time stamp is generated andbounded to the new route. The route will be aged out when the timerexpires. If the unicast route entry for the initiator is already there,the route will be updated. The timer is refreshed as well.

In FIG. 2, the star A is the initiator of the query; the balls representthe routers within a Wireless Sensor Network; the node H is the targeteddevice of the query; the straight arrows show the directions of thebroadcast; the curved arrows show the direction of the best unicast paththat is created during the broadcast. The node H is expected to use thenewly created unicast path to send its response messages to querist A.

Each node has a node ID in a WSN. Because a network address is uniquewithin a WSN, it is used as a node ID. A specific sequence number isgenerated and associated with each message in the node that initiatesthe message. The combination of a node ID and sequence number uniquelyidentifies a broadcast or unicast packet. This pair is stored in therouting entry, and is used to identify and prevent the broadcast loop orrepeated forwarding. Upon receiving a broadcast packet, the node does anacceptance and loop check by looking at the pair. If the packet does notpass acceptance and loop check, it is discarded quietly without anyfurther actions. Otherwise, the node remembers the pair and the processcontinues.

In the prior art, there are a number of traditional ways to preventbroadcast loop. The simplest way is to keep track the number of hops apacket has traveled. The packet is discarded if it reaches a threshold.Another way is to add the address of every node traveled to the packet.The packet is discarded if the current node is in the traveled list.

The first way is essentially a damage control, the loop might happen,but is the extent of the loop is under control. The second approachstops the loop completely, but the overhead is considerable because thesize of a packet is usually limited in a WSN.

The loop detection mechanism in this invention does not havedisadvantages from either of the approaches traditional approaches. Ifan originator's ID and the sequence number matches with existing pairand the cost to arrive current node is larger, the incoming packet iseither from a worse path or from a loop. See FIG. 11 and furtherdiscussion below.

FIG. 11 shows the procedures of the acceptance and loop check, and howan incoming broadcast packet is processed. If the ID of the packet'soriginator is not in the routing entry, a new entry and its timer (ortime stamp) is created. The sequence number is stored. If the currentnode is the target node, the packet is sent to the application modulefor further processing. Otherwise, broadcast continues. If theoriginator's ID is already in the routing entry, but the sequence numberis smaller than stored number, this packet is too old, and will bediscarded. If the sequence number is greater than the stored number, thepacket will be processed by routing module for routing update. If thecurrent node is the targeted node, the packet is sent to the applicationmodule for further processing, otherwise, the broadcast continues.

If the sequence number exists, but the cost to arrive at the currentnode is bigger based on the routing section of the packet, it is from aloop or a worse path, the packet is discarded. If the cost is smaller,the packet will be processed by the routing module for routing update.If the current node is the targeted node, the packet is sent to theapplication module for further processing, otherwise, the broadcastcontinues.

A coordinator or destination node can receive multiple copies of a samepacket from a single broadcasting cycle. This is due to the fact offlooding. Flooding is a waste to some extent. In this invention, themultiple copies will be used for reliability purpose that increases thesuccessful rate in terms of packet delivery. If the coordinator orinitiator fails to receive the responses from a recipient within apredefined time period, the initiator resends the query messages to therecipient.

For an event driven message, the packet will transferred to thecoordinator or destination via a unicast route if such a route exists.Otherwise, the broadcast is performed and a unicast best route towardthe initiator can be optionally created as it is described previously.The event message is propagated from a node to its adjacent node untilreaching the coordinator or destination node.

In FIG. 2, although the node H is the target node of the query, everynode that traveled by the broadcast query message takes this opportunityto generate the best routing entry for initiator A. As a result, amultipoint to point unicast tree rooted at the initiator is created.

One embodiment of this process is shown in FIG. 3. The star is theinitiator of the querist; the balls are the nodes in the Wireless SensorNetwork; the node H is the targeted node of the query; the straightarrows show the directions of the unicast path, they form a multipointto point tree. While delivering the query message to the destination,the broadcast is really a route advertisement for initiator A, becausethe broadcast messages are the hybrid packets that carry both routinginformation and user data.

As it is described previously, the new routing entry will be aged outand removed eventually. If the unicast route is for the coordinator, itmight be treated differently. For example the time interval for agingout might be longer. In that case, an unsolicited event has a betterchance to use a unicast path to deliver event message to thecoordinator. This is an optimization. However, this is not recommendedin a mobile WSN. A unicast route might become stale quickly in a dynamicmobile environment. The event message could be sent to nowhere with astale route.

This invention supports a mobile WSN where every node is allowed to movein any direction. With this solution, the regular routing advertisementand maintenance is excluded. The task of keeping track of the mobileroutes is eliminated. On the other hand, a broadcast packet shouldalways catch a mobile node somewhere as long as the node is locatedwithin the WSN. This allows a mobile node to catch the fresh route withless delay. Therefore, a response message always uses a newly created orupdated unicast route.

In FIG. 4, node A is an arbitrary node in a WSN. It was originallylocated in top left corner. If node A is near that spot when a broadcastpacket arrives, node B advertises the broadcast packet to it andreceives the response message from it. If node A moves to the lower leftcorner when broadcast packet arrives, node C will advertise thebroadcast packet to it and will receive the response message from it.

This invention introduces a new concept called a data vehicle, and mayalso be referred to as a moving container. A data vehicle is a newmethod to do packet aggregation over a Wireless Sensor Network.

When a WSN node is ready to send a packet to the coordinator, it cancreate a data vehicle and load the message onto the vehicle. Thismessage is the first rider, called the original message. The datavehicle might go out of the air via unicast routes or broadcastforwarding, but the unicast forwarding is the first choice as long asthe unicast route is available. During the propagation, the messagesfrom the relay nodes are allowed to get on the vehicle and be forwardedto the destination along with the rest of the messages on the vehicle.As a result, the coordinator is able to receive a list of messages froma single packet. Such aggregation processes may vary from application toapplication and can be constrained by the specific limitations of theWSN such as a packet size or maximum transmission unit (MTU). Theaggregation is beneficial because it greatly reduces the number ofactive packets in a Wireless Sensor Network and reduces the sending andreceiving operations that consume significant amounts of electric power.It should be noted that to transmit a packet consumes several times ofelectrics of a CPU consumes at same amount of time. Therefore, the fewerpackets sent, the better.

This aggregation is in a loose manner. It is an option, not mandatory. Amessage can choose to take a ride from data vehicle, or go out of air byitself. This is similar to a real world bus, one might choose to get ona bus if it arrives at a good timing and the destination matches. Youmight not wait a bus if it takes too long. On the other hand, since thepacket length is limited in a WSN, a message might not have a chance toget on a particular data vehicle. This is also similar to a real worldbus that is full, which can not take more passengers.

There are two types of data vehicles in this invention: a query specificdata vehicle and a wild card data vehicle. The former is used to collectresponse messages after the coordinator issues a query to multiple nodesor all the nodes. This data vehicle is marked as vehicle_q that followsa unicast path. The latter is used to collect any response messages andunsolicited event reports for the coordinator. This data vehicle ismarked as vehicle_w that might be forwarded via broadcast or unicast,but unicast is the first choice.

For a wild card data vehicle, each unsolicited event message on thevehicle may be reviewed and processed by each node that is traveled toby the vehicle. The acceptance check and loop check will be performed oneach message of the data vehicle. This is the same as if an unsolicitedevent message arrives on a random node. As a result, the message mightbe removed from the vehicle and be discarded. At extreme case, if thevehicle becomes empty then the vehicle is discarded as a whole.

For a query driven broadcast, the coordinator or a specific nodeinitiates a query message that is broadcasted to the WSN. During thepropagation, a unicast route toward the initiator is created. Theresponses from targeted nodes are forwarded to the initiator via theunicast routes.

If the query is sent to multiple nodes, an aggregation process isoptionally performed for the responses. In this invention, the responsemessages are picked up by the query specific data vehicle when thepacket is on its way toward the querist.

To do that, the targeted node refrains from replying to the query rightaway. Instead, the node creates a response message and an instance of aquery specific data vehicle. This message gets on the vehicle as anoriginal message. A timer or time stamp is created for the vehicle. Whenthe timer fires, the vehicle goes out of the air and starts to collectresponse messages from other nodes on its way toward the coordinator.

FIG. 5 shows the processes that are taken when a node receives a querymessage from the coordinator. As it is described previously, a typicalquery message arrives on a node via broadcast. An acceptance and loopcheck process is taken by looking at its source address and the sequencenumber of the message. If it does not pass the check, then the messageis discarded. Otherwise, the routing module will process the querymessage by looking at routing section of the message. A routing entryfor the coordinator might be created. If the current node is not therecipient, this message is sent via a unicast if that is applicable.Otherwise, it will be sent via broadcast or a multicast. The unicast isapplicable if the destination of the message is a single node and aunicast route entry is available in current node.

If the current node is one of the recipients then the query message isforwarded to the application layer for further processing. If thecurrent node is the only recipient, a response message will be sentimmediately via the unicast route that is created by the broadcast. Ifthe query message is destined for a number of nodes, then a responsemessage and a query specific data vehicle are created. This vehicle iscalled vehicle_q2 here. A timer or a time stamp is also generated forvehicle_q2. The query message is then sent out via broadcast ormulticast.

FIG. 6 shows the processes that are taken when a query data vehiclearrives on local node. Say it is vehicle_q1. Note that vehicle_q1follows a unicast path that was newly created. If the correspondingvehicle_q2 for the same query (see FIG. 5) does not exist, thenvehicle_q1 is sent immediately. The vehicle_q2 is not there for one ofthe two reasons: either the current node is not the recipient of theoriginal query message, or the current node is the recipient, but theresponse message is already sent. If the corresponding vehicle_q2 doespresent, then the current node is one of the recipients and vehicle_q2'stimer has not expired yet. In that case, if the total length of bothvehicles great than local MTU value, the vehicle_q1 is sent immediately.The vehicle_q2 will wait for timer expiration or next incoming vehicle.If the sum is less than MTU value, then the messages on the vehicle_q2will be moved to vehicle_q1. The vehicle_q2's timer will be canceled,and vehicle_q2 will be discarded. The vehicle_q1 is then sent viaunicast path.

FIG. 7 shows the processes that are taken when vehicle_q2's timer fires.The vehicle_q2 will be sent via unicast path that is generated when theoriginal query message was processed.

For a wild card process, the messages on the data vehicle could beresponse messages or unsolicited event messages. In both cases, thedestination of the messages is usually the coordinator. For eachunsolicited event message on the vehicle, a unicast best route towardthe initiator of the event message can be optionally created during thebroadcast of the vehicle. If the option is enabled, each event messageon the vehicle is processed by a routing module. The unicast routestoward event senders might be installed in the routing table. This isthe same as receiving the unsolicited event message individually.

FIG. 8 shows the processes that are taken when a message is ready to besent out. The message could be a response message or an unsolicitedevent message. If a wild card data vehicle for the destination of themessage is not available, an instance of such a vehicle is created. Thevehicle is called vehicle_w2. The message gets on the vehicle as anoriginal message, and a timer or a time stamp is created for thevehicle. If a wild card data vehicle for the same destination is alreadythere, the message gets on the vehicle immediately. If the total lengthof the vehicle plus the maximum length of a response message or eventmessage exceeds MTU value, the timer is canceled and the vehicle departsimmediately since the room left on the vehicle might not enough for thenext message.

FIG. 9 shows the processes that are taken when a wild card data vehiclearrives on current node. Let's call it vehicle_w1. Each event message onvehicle_w1 will be reviewed for an acceptance and loop check. As aresult, the messages might be discarded. If all the messages are to bediscarded, the vehicle will be discarded as well. The remaining eventmessages will be processed by routing module. The unicast routes towardevent senders might be optionally installed in the routing table. If avehicle_w2 for the same destination of vehicle_w1 does not exist,vehicle_w1 is sent immediately. If such a vehicle_w2 presents and thetotal length of both vehicles is great than local MTU value, thevehicle_w1 is sent. The vehicle_w2 will wait for timer expiration oranother incoming vehicle, whichever comes first. If the total length ofboth vehicles is less than MTU value, then vehicle_w2's messages aremoved to vehicle_w1. The vehicle_w2 is discarded and its timer iscanceled. The vehicle_w1 are sent afterwards.

FIG. 10 shows the processes that are taken when vehicle_w2's timerfires. The vehicle_w2 will be sent via unicast path if it exists,otherwise it is broadcasted.

While several variations of the present invention have been illustratedby way of example in preferred or particular embodiments, it is apparentthat further embodiments could be developed within the spirit and scopeof the present invention, or the inventive concept thereof. However, itis to be expressly understood that such modifications and adaptationsare within the spirit and scope of the present invention, and areinclusive, but not limited to the following appended claims as setforth.

What is claimed is:
 1. A method of hybrid routing and forwarding for awireless sensor network comprising the steps of: broadcasting by aninitiator node of the wireless sensor network, a broadcast packetcontaining both a quantity of user data, and a quantity of routingadvertisement data; forming a unicast route to the initiator node by asecond node based on the quantity of routing advertisement data of thebroadcast packet; receiving the quantity of user data of the broadcastpacket by the second node; propagating the quantity of routingadvertisement by the initiator node on an as-needed basis, wherein thequantity of routing advertisement data is incorporated into a packetcontaining the quantity of user data whenever the quantity of user datais broadcast; and processing by the second node, the broadcast packet toeliminate a broadcast loop.
 2. The method of hybrid routing andforwarding for a wireless sensor network of claim 1 further comprisingthe steps of: operating the initiator node and the second node as lowpower, low bandwidth wireless devices; and moving at least one of theinitiator node and the second node from a first location to a secondlocation.
 3. The method of hybrid routing and forwarding for a wirelesssensor network of claim 1 further comprising the step of forming aunicast route to the initiator node by the second node using a smartmetric.
 4. The method of hybrid routing and forwarding for a wirelesssensor network of claim 1 wherein the step of propagating the quantityof routing advertisement is performed on an event-driven as needed basiswherein an event recorded by a sensor at the initiator node creates thequantity of user data broadcasted by the initiator node.
 5. The methodof hybrid routing and forwarding for a wireless sensor network of claim1 wherein the step of propagating the quantity of routing advertisementis performed on a query driven as needed basis wherein the user data ofthe broadcast packet is a query directed to the second node.
 6. Themethod of hybrid routing and forwarding for a wireless sensor network ofclaim 1 wherein the step of processing by the second node the broadcastpacket to eliminate a broadcast loop further comprises the steps of:determining that an originator ID of the broadcast packet is in arouting table of the second node; determining that a sequence number ofthe broadcast packet is in the routing table of the second node;determining that the route cost is greater than an existing route; anddiscarding the packet.
 7. The method of hybrid routing and forwardingfor a wireless sensor network of claim 1 further comprising the step ofincreasing reliability by utilizing a broadcast overlap formed by thestep of broadcasting by an initiator node.
 8. The method of hybridrouting and forwarding for a wireless sensor network of claim 1 furthercomprising the step of broadcasting, by the second node, a secondquantity of user data and a second quantity of routing advertisementdata in the event that the unicast route formed ages out.
 9. The methodof hybrid routing and forwarding for a wireless sensor network of claim1 further comprising the step of forming a data vehicle packet by thesecond node to follow the unicast route to the initiator node; andforming a timer for the data vehicle packet by the second node.
 10. Themethod of hybrid routing and forwarding for a wireless sensor network ofclaim 9 further comprising the step of adding a quantity of datadestined for the initiator node to the data vehicle packet by a thirdnode.
 11. The method of hybrid routing and forwarding for a wirelesssensor network of claim 1 further comprising the step of forming a datavehicle packet by the second node to be broadcast to the initiator node;and forming a timer for the data vehicle packet by the second node. 12.The method of hybrid routing and forwarding for a wireless sensornetwork of claim 11 further comprising the step of adding a quantity ofdata destined for the initiator node to the data vehicle packet by athird node; adding a quantity of routing advertisement data to the datavehicle packet; and forming a second unicast route by the third node tothe initiator node.
 13. The method of hybrid routing and forwarding fora wireless sensor network of claim 12 further comprising the step ofprocessing, by the third node, the data vehicle packet to eliminate abroadcast loop.
 14. The method of hybrid routing and forwarding for awireless sensor network of claim 9 further comprising the step oflimiting the quantity of user data storeable in the data vehicle by themaximum transition unit of the wireless sensor network.
 15. A method ofhybrid routing and forwarding for a mobile wireless sensor networkutilizing a query specific data vehicle comprising the steps of:broadcasting a query, by a coordinator node, to a plurality of nodes ofa wireless sensor network, the query being sent in a broadcast packetcomprising a quantity of route advertisement data; forming a unicastroute to the coordinator node by one of the plurality of nodes based onthe quantity of route advertisement data sent in the broadcast packet;forming the query specific data vehicle by the one of the plurality ofnodes; forming a timer for the query specific data vehicle by the one ofthe plurality of nodes; inserting a quantity of user data into the queryspecific data vehicle by the one of the plurality of nodes, the quantityof user data being destined for the coordinator node; sending the queryspecific data vehicle along the unicast route; receiving the queryspecific data vehicle by another of the plurality of nodes; andinserting a second quantity of user data into the query specific datavehicle by the another one of the plurality of nodes, the secondquantity of user data being destined for the coordinator node.
 16. Themethod of hybrid routing and forwarding for a wireless sensor networkutilizing a query specific data vehicle of claim 15 further comprisingthe steps of: forming a second query specific data vehicle by theanother of the plurality of nodes; forming a second timer for the secondquery specific data vehicle by the another of the plurality of nodes;inserting the second quantity of user data into the second queryspecific data vehicle; and determining if the second quantity of userdata can be inserted into the query specific data vehicle based on amaximum transfer unit value of the wireless sensor network.
 17. A methodof hybrid routing and forwarding for a wireless sensor network utilizinga wild card data vehicle comprising the steps of: sensing an recordableevent by a wireless sensor node; creating a quantity of user data basedon the sensing of the recordable event by the wireless sensor node;forming a wild card data vehicle by the wireless sensor node; insertingthe quantity of user data formed by the wireless sensor node into thewild card data vehicle, the quantity of user data being destined for acoordinator node; forming a timer for the wild card data vehicle by thewireless sensor node; broadcasting the wild card data vehicle by thewireless sensor node to a second wireless sensor node; and receiving thewild card data vehicle by the second wireless sensor node.
 18. Themethod of hybrid routing and forwarding for a wireless sensor networkutilizing a wild card data vehicle comprising of claim 17 furthercomprising the steps of: inserting a quantity of route advertisementdata into the wild card data vehicle by the wireless sensor node; andforming a unicast route to the coordinator node by the second wirelesssensor node based on the quantity of route advertisement data sent inthe wild card data vehicle.
 19. The method of hybrid routing andforwarding for a wireless sensor network utilizing a wild card datavehicle comprising of claim 18 further comprising the steps of: forminga second wild card data vehicle by the second wireless sensor node;forming a second timer for the second wild card data vehicle by thesecond wireless sensor node; inserting the second quantity of user datainto the second wireless sensor node; determining if the second quantityof user data can be inserted into the wild card data vehicle based on amaximum transfer unit value of the wireless sensor network.
 20. Themethod of hybrid routing and forwarding for a wireless sensor networkutilizing a wild card data vehicle comprising of claim 19 furthercomprising the step of processing the wild card data vehicle by thesecond wireless network node to prevent a message loop, whereby eachquantity of data of the wild card data vehicle are processedindividually.